Recently, there has been increasing interest in minimally invasive and percutaneous replacement of cardiac valves. Percutaneous replacement of a heart valve does not involve actual physical removal of the diseased or injured heart valve. Rather, the defective or injured heart valve typically remains in position while the replacement valve is inserted into a balloon catheter and delivered percutaneously via the vascular system to the location of the failed pulmonary valve. Such surgical techniques involve making a very small opening in the skin of the patient into which a valve assembly is inserted via a delivery device similar to a catheter. There, the replacement valve is expanded by the balloon to compress the native valve leaflets against the body opening in which it is inserted, anchoring and sealing the replacement valve. This technique is often preferable to more invasive forms of surgery, such as opening a large portion of the chest for cardiopulmonary bypass, for example.
In the context of percutaneous, pulmonary valve replacement, U.S. Patent Application Publication Nos. 2003/0199971 A1 and 2003/0199963 A1, both filed by Tower, et al., describe a valved segment of bovine jugular vein, mounted within an expandable stent, for use as a replacement pulmonary valve. The replacement valve is crimped or compressed around the balloon portion of a catheter until it is as close to the diameter of the catheter as possible. The valve is then delivered percutaneously via the vascular system to the location of the failed pulmonary valve and expanded by the balloon to compress the valve leaflets against the right ventricular outflow tract, anchoring and sealing the replacement valve. As described in the articles: “Percutaneous Insertion of the Pulmonary Valve”, Bonhoeffer, et al., Journal of the American College of Cardiology 2002; 39: 1664-1669 and “Transcatheter Replacement of a Bovine Valve in Pulmonary Position”, Bonhoeffer, et al., Circulation 2000; 102: 813-816, the replacement pulmonary valve may be implanted to replace native pulmonary valves or prosthetic pulmonary valves located in valved conduits. Other implantables and implant delivery devices also are disclosed in published U.S. Pat. Application No. 2003/0036791 A1 and European Patent Application No. 1 057 460-A1.
Assignee's co-pending U.S. patent application titled “Apparatus for Treatment of Cardiac Valves and Method of Its Manufacture”, filed Nov. 18, 2005 and assigned U.S. Ser. No. 11/282,275, describes percutaneous heart valves for use as a replacement pulmonary valve. Like the valves described by Tower et al., the heart valves of this co-pending application incorporate a valved segment of bovine jugular vein, mounted within an expandable stent.
In addition to percutaneous valve implantation, heart valve repair can also be accomplished using catheter-based valve repair procedures. In the context of annuloplasty ring implantation on a valve annulus, for example, a variety of repair procedures can be used, such as procedures that require indirect visualization techniques to determine the exact location of the heart valve and annuloplasty ring during placement of the ring at the valve annulus. Indirect visualization techniques, as described herein, are techniques that can be used for viewing an indirect image of body tissues and/or devices within a patient. One example of such a technique is referred to as endoscopic visualization, which involves displaying images from endoscopic light guides and cameras within the thoracic cavity on a video monitor that is viewed by a surgeon. Effective use of this method depends on having sufficient open space within the working area of the patient's body to allow the surgeon to recognize the anatomical location and identity of the structures viewed on the video display, which can be difficult to accomplish in certain areas of the heart.
Another indirect visualization technique involves the use of fluoroscopy, which is an imaging technique commonly used by physicians to obtain real-time images of the internal structures of a patient through the use of a fluoroscope. Fluoroscopy can be effective in many situations, but does have some drawbacks. For one example, some tissues, such as the cardiac tissues, do not readily appear under fluoroscopy, making it very difficult to accurately align an annuloplasty ring prior to its implantation. To improve the visualization of the area of interest, radiopaque contrast dye can be used with x-ray imaging equipment. However, when treating the mitral valve, for example, repeated injections of contrast dye are not practical because of rapid wash-out of the dye in this area of high fluid flow. For another example, to make high-volume contrast injections of this kind, an annuloplasty catheter system would require multiple lumens, undesirably large lumens, and/or an additional catheter, none of which is desirable during catheterization procedures. Further, multiple high-volume contrast injections are somewhat undesirable for the patient due to potential complications in the renal system, where the radiopaque contrast medium is filtered from the blood.
A wide variety of other techniques are available for viewing images of cardiac structures, including ultrasonography such as trans-thoracic echocardiography (TTE), trans-esophageal echocardiography (TEE), cardiac magnetic resonance (CMR) including magnetic resonance imaging (MRI) or magnetic resonance angiography (MRA), and computed tomography (CT) including computer tomography angiography (CTA). These techniques, used alone or in combination with other available techniques, all typically have certain drawbacks relative to visualization and guidance during catheter-based valve repair procedures.
Yet another visualization technique that can be used for catheter-based valve repair involves mapping a valve annulus, such as a mitral valve annulus, and obtaining real time imaging during heating heart surgery through the use of electromagnetic (EM) imaging and navigation. This type of technique can be effective for viewing the significant movement of the annulus during both systole and diastole that occurs during procedures performed on a beating heart. With EM navigation, a patient is generally placed on a table having a plurality of sensors either on the surface of the table or at positions around the table. The sensors are connected to a processor and the processor knows the positions of the sensors relative to the table. A patient is then placed on the table and immobilized, and then an elongated flexible device having at least three EM coils spaced along its distal portion can then be inserted into the patient's body (into the vascular system for example). The coils are typically made from extremely small diameter material that can be wound around the outside of the device or wound around an interior layer of the device and then covered with an additional layer of material. A very thin wire or some other electrically conductive material can be used to communicate from an external AC power source to each of these coils. Alternatively, wireless sensors can be used to eliminate the need to provide a wire to communicate with the EM coils.
As the elongated device is moved through the body, the sensors can detect the EM signal that is created by the moving coil. The processor then calculates the position of the coils relative to each sensor. The location of the sensors can be viewed on a display device, and the EM navigation can be combined with other navigation/visualization technologies so that the location of the EM coils in a patient's body can be viewed in real time. Additional sensors may also be incorporated into a system using EM navigation to improve the accuracy of the system, such as temporarily attaching sensors to a patient's body and/or covering at least a portion of a patient with a blanket that contains additional sensors. The relationship between all of the sensors can be used to produce the image of the patient's body on the table. Examples of methods and systems for performing medical procedures using EM navigation and visualization systems for at least part of an overall navigation and visualization system can be found, for example, in U.S. Pat. No. 5,782,765 (Jonkman); U.S. Pat. No. 6,235,038 (Hunter et al.); U.S. Pat. No. 6,546,271 (Resifeld); U.S. Patent Application No. 2001/0011175 (Hunter et al.); U.S. Patent Application No. 2004/0097805, (Verard et al.), and U.S. Patent Application No. 2004/0097806 (Hunter et al.), the entire contents of which are incorporated herein by reference.
Another method for mapping the mitral valve annulus and obtaining real time imaging during beating heart surgery is through the use of electro-potential navigation. Electro-potential (EP) navigation involves the use of external sensors that are placed on the patient. When using EP navigation, a low frequency electrical field is created around the patient, and the coils on the instrument are connected to a DC energy source such that there is a constant energy signal emitting from the coils. The coils create a disturbance in the electrical field as they move through the field, and location of the instrument in the 3D coordinate space is calculated by determining the location of the disturbance in the energy field relative to the sensors.
As described above, delivery of a valve percutaneously to a remote access site in the body via the vascular system and delivery of devices for treating cardiac valve disease can be challenging because precise manipulation of the surgical tools is more difficult when the surgeon cannot see the area that is being accessed and when the heart is moving. Thus, there is a need for heart valve placement or repair systems having visualization capabilities that permit the surgeon to quickly, easily and securely implant a heart valve or repair a heart valve in a patient with minimal resulting trauma to the patient. In certain cases, there is a further need for heart valve placement systems that can implant such valves into a failed bioprosthesis, which also requires precise manipulation by a surgeon. In addition, there is a need for heart valve repair systems that can repair a failed or failing heart valve or a failed or failing bioprothesis. Such systems should further provide the surgeon with a high degree of confidence that a valve has been properly positioned within the patient's heart during surgery.